1. Field of the Invention
The present invention relates to an organic luminescent device, and particularly to an organic luminescent device with improved light extraction efficiency.
2. Description of the Related Art
In recent years, an organic electroluminescence (EL) device known as an organic luminescent device has been developed for practical use from a viewpoint of its application to display and illumination. An organic EL device is a device configured so that a thin-film luminescent layer made of an organic compound is held between electrodes on a substrate made of a glass or the like, and configured to emit light by supplying an electric current between the electrodes.
When an organic EL device is used as a light source for illumination or the like, it is necessary to extract emitted light to the outside as much as possible. However, in a conventional organic luminescent device, approximately 80% of emitted light is absorbed by the glass substrate and the luminescent layer, and only the remaining approximately 20% of the light can be extracted to the outside.
FIG. 9 shows an example of a structure of a conventional organic EL device. In this organic EL device 30, an anode 2, an organic luminescent layer 3 and a cathode 4 are formed in lamination on a glass substrate 1, and are sealed by a glass-made sealing plate 8 on the glass substrate 1 with a seal resin 10 adhesively interposed therebetween. Concave and convex portions are formed on an outer surface of the glass substrate 1 that is opposed to the luminescent area thereof. This structure prevents the emitted light from being totally reflected, trapped and absorbed in the glass substrate 1, so that light extraction efficiency is improved.
Furthermore, there has been disclosed an organic EL device in which a lens layer is provided between the luminescent layer and the substrate while concave and convex portions are provided on an interface between the substrate and the lens layer (see Japanese Patent Application Publication No. 2006-269328, for instance). With this structure, the concave and convex portions formed on the interface prevent total reflection on the interface between the lens layer and the substrate, so that light extraction efficiency is improved.
However, there has been a problem that, generally, light radiating from the luminescent area is repeatedly propagated and reflected to be absorbed by the glass substrate and the seal resin, thereby turning into heat.
In addition, when multiple organic EL light sources are used as a back light source, connection areas thereof emit no light. As a result, uneven light is emitted from the light source. On the other hand, if a diffusion plate or the like is used to cover the connection areas, the light source itself is inevitably made thicker. In this case, another problem arises that the characteristic thin shape of the organic EL device cannot be utilized fully.